The invention is an improvement of levelling systems using pendulum-type apparatus to determine a horizontal position with respect to an opposite grade rail. Such systems are well known to the railroad industry and have been in use for many years. Such systems typically use a horizontal reference beam which is transmitted over the track being tamped, for example. The track is jacked parallel to a reference beam to provide 100% error corrections. Such systems utilize a modulated cone of light, from one of two infra- red projectors (one located over each rail) and selected over the grade rail, which is transmitted over a shadowboard calibrated to the top of both rails of the tie being tamped, into two receivers referenced to the tamped track at the rear of the machine, one receiver being located over each rail. The track and the shadow board are raised until the beam is intercepted at the selected height.
Typically, the receiver of the grade rail is calibrated directly to the top of the rail at the rear wheels of the machine. The cross-level receiver "floats" at all times regardless of track conditions, and is controlled with a fully automatic and precision designed pendulum arrangement to maintain a horizontal position with respect to the opposite grade rail. Such levelling systems are capable of accuracy within plus or minus 1/31" (1 mm) on the track.
Such pendulum type levelling systems are typically used with jack tampers, which are automated to the extent that the operator can select the desired raise and elevation.
The output of such a levelling system activates either one of two lead screw mechanisms located respectively at opposite ends of a platform on which is mounted the pendulum, to maintain the platform level by controlling the actuation of a respective one of the lead screws.
Such pendulum-type levelling systems are subject to many disadvantages, such as the need to maintain the oil in the pendulum mechanism, which oil is subject to wide viscosity changes resulting from the great temperature ranges over which the levelling system is required to operate. The pendulum-type levelling system is also bulky and heavy.
There is thus a need for an improved type levelling system to overcome the aforementioned disadvantages as well as to provide improved capability for track levelling operations.